1. Field of the Invention
The present invention relates in general to wide angle projection display systems and in particular to an apparatus for displaying an image over most of the surface of a spherical or other three-dimensional screen.
2. Description of Related Art
A rear projection system projects an image onto a rear surface of a translucent screen to produce a display on the front surface of the screen. Various prior art projection systems produce displays on a spherical, hemispherical or other three- dimensional rear-projection screens. U.S. Pat. No. 2,592,444 issued Apr. 8, 1952 to Matelena describes an apparatus employing a projector having two opposed lens mounted inside a sphere for projecting images onto opposing sides of the sphere. The sphere is formed of translucent material so that the image appears on the outer surface of the sphere. U.S. Pat. No. 3,586,432 issued Apr. 1, 1969 to Pentes describes a system employing a set of three projectors mounted inside a translucent sphere. Both of these systems provide only very limited coverage of the full spherical screen and have the added difficulty of access to the projectors mounted inside the sphere.
It is known to employ a projector having a xe2x80x9cfisheyexe2x80x9d lens to directly project a display on a hemispherical screen, however a single such a projector cannot distribute an image over a spherical screen. U.S. Pat. No. 4,859,053 issued Aug. 22, 1989 to Nicolas describes a system for producing an image on a hemispherical portion of a sphere. A projector positioned outside the sphere projects the image onto the inner side of a translucent hemisphere of the sphere through an aperture in a side of the sphere opposite the translucent hemisphere. This system provides easy access to the projector, but it only produces an image on a hemispherical screen.
U.S. Pat. No. 4,427,274 describes a front-projection system employing two projectors positioned external to a sphere for projecting images through apertures on opposite sides of the sphere onto inner surfaces on opposing hemispheres. A rear projection system employing similar principles could produce a display over most of the surface of a spherical rear-projection screen. However such a system employing externally mounted projectors at opposite ends of the sphere which would detract from the appearance of the display. A system employing an externally mounted projector(s) at only one end of a sphere would be aesthetically preferable.
All of the above system can produce xe2x80x9cghost imagesxe2x80x9d if a portion of an image to be projected outward from the screen surface is reflected inward from the inner surface and falls onto another portion of the inner surface of the sphere.
What is needed is a rear-projection system capable of producing a display over most of the outer surface of a sphere resting on a base, which requires projection equipment mounted only within the base and which suppresses ghost images.
A projection system in accordance with the invention produces a display on a front-projection or a rear-projection screen having an inner surface substantially enclosing a three-dimensional space. The projection system employs a convex mirror positioned within the three-dimensional space to reflect an image produced by a projector. The mirror disperses the image over the inner surface of the screen. When the screen is formed of translucent material, the image appears on the screen""s outer surface so that it may be viewed from outside the enclosed spaced. When the screen""s inner surface is opaque, the image may be viewed on the screen""s inner surface from within the three-dimensional space. Images produced by the projector may be appropriately pre-distorted to compensate for any distortion caused by the screen and dispersing mirror geometry so that they appear correctly when projected on the screen.
One embodiment of the invention employs a spherical translucent screen residing on a base containing a projector which projects an image through an aperture in the screen. A convex mirror mounted within the enclosed three-dimensional space disperses the projected image by reflecting it over most of the inner surface of the rear-projection screen, thereby producing a rear-projected image over most of the outer surface of the sphere. Only two relatively small regions of the screen lying along the axis of projection are obscured. A non-reflective baffle may be mounted within the sphere to absorb reflections from the sphere""s inner surface to prevent ghost images.
An alternative embodiment of the invention employs two projectors mounted within the base, each of which projects a separate image into the space enclosed by the screen. A convex lower surface of a first mirror mounted near the center of the space reflects the image from the first projector onto a lower half of the inner surface of the screen. A second mirror mounted near the top of the space in opposition to the base reflects the image produced by the second projector onto a second convex reflector mounted near the center of the space and oriented upward which in turn reflects that image over the upper half of the inner surface of the screen. The two projector version produces a brighter display with more image detail than the single projector version of the display system.
Other embodiments of the invention employ one or more convex mirrors to disperse images from one or more projectors over inner surfaces of hemispherical screens.
It is accordingly an object of the invention to provide a system for producing a display over most of the surface of a three-dimensional screen, most particularly a spherical rear projection screen.
The claims portion of this specification particularly points out and distinctly claims the subject matter of the present invention. However those skilled in the art will best understand both the organization and method of operation of the invention, together with further advantages and objects thereof, by reading the remaining portions of the specification in view of the accompanying drawing(s) wherein like reference characters refer to like elements.